R: R: Pointing large dishes

Bob,
Pointing at +7 degrees at apogee ( 16 hours) with a 35 dBi gain dish in
polar mount it make to receive a very strong noise generated and translated
by the transponder itself in the order of 10 dB or more above the noise
floor of a 1 dB overall NF receiving system.
As soon the transponder noise is received with a 3 dB (S+N)/N ratio on the
ground the S/N ratio do not improve any more because increasing the dish
diameter both signal and noise increases by the same level .
Having a 35 dBi gain dish with polar mount i would prefere to chouse a
pointing compromise less than +7 degrees in order to receive the AO40
beacon and its TLM all the orbit available time because TLM is also
important at perigee.
Pointing at +7 degrees at apogee with a 3 degrees pencil at -3dB points it
make to receive the same S/N at apogee and nothing about at perigee when the
SSP latitude is -7 degrees because the dish off point at perigee will be 14
degrees.
73" de i8CVS Domenico
----- Original Message -----
From: Bob Bruninga <bruninga@usna.edu>
To: i8cvs <domenico.i8cvs@tin.it>
Cc: Roger <rogermj01@attbi.com>; AMSAT-BB <amsat-bb@AMSAT.Org>
Sent: Thursday, August 01, 2002 2:52 PM
Subject: Re: R: [amsat-bb] Pointing large dishes
On Thu, 1 Aug 2002, i8cvs wrote:
> A 10' ( 3 meters) dish at 2400 MHz has a lobe like a pencil of 3 degrees
> at - 3 dB points.
>
> Since the AO40 inclination is 7.53 degrees the satellite subpoint latitude
> will change from -7.53° South to + 7.53 North during one orbit.
But ALL the time at Apogee (16 hours) is +7 degrees and it is only at -7
during Perogee. Not worth worrying about... So just set for APOGEE..
See the three links in the 3rd line down on my WEB page for photos:
http://www.ew.usna.edu/~bruninga/sitemap.html
No, I have NOT gone back and actually finished the project. Winter snow
and then work got in the way...
bob
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